This study aims at localizing and characterizing the components of arterial ground substance, with initial emphasis on proteoglycans. Localization at the electron microscope level of resolution will employ histochemistry, before and after enzyme digestion, immunocytochemistry, and extractability studies. Characterization of proteoglycans will be done on materials extracted with high molar guanidine chloride and will employ equilibrium density gradient centrifugation followed by sugar and protein analysis, immunologic studies on various fractions, analytical ultracentrifugation to study physical properties, and high resolution electron microscopy.